The present invention relates in general to a film cassette for use in connection with a photographic camera and, in particular, to a film cassette of the type having a supply-or main part for accommodating a film supply and an insert part detachable from the supply part and including a film take-up spool whereby in the attached or sealing position the two parts of the cassette form a light-tight housing unit.
The cassette of this type has the advantage that it is compact and space saving, has a flat configuration and consequently it can be easily handled by the operator of the camera. Such a cassette can be operated without any additional light enclosures and consequently it can be readily installed in and withdrawn from the camera. The insertion of the film supply into the cassette is simple and can be made by the user himself and consequently the selection and exchange of the film is considerably facilitated.
In a known film cassette of similar type the cassette is first inserted into the camera whereupon the detachable insert part of the cassette is gripped by the camera mechanism and is dispatched into an end position during each cocking of the shutter and the advance of the film past the film window. In doing so, a certain film length is withdrawn from the supply reel arranged in the supply or main part of the cassette and is positioned behind the film gate or window. The film gate is formed in a film compression frame which is shiftable in the direction of the optical axis and presses the film against a film compression plate. Upon the release of the camera shutter the film compression frame is again withdrawn from the film compression frame and gives way for the repeated passage of the cassette insert part. At the same time. The insert part is again moved by the action of a drive back into its starting position in contact with the supply part of the cassette. Simultaneously the drive rotates the film take-up spool and the exposed portion of the film is wound up on the take-up spool. During the new cocking of the camera shutter and during the actuation of the film advance lever the above-described process is repeated whereby during the travel of the insert part of the cassette into its detached end position the film take-up spool is arrested in the direction opposite to that of the film winding so that the film could not be withdrawn from the take-up spool.
This known film cassette necessitates, however, a very complicated winding mechanism in the camera inasmuch as during each photographic shot the cassette insert part has to be moved back and forth relative to the cassette film supply part irrespective of the fact whether the cassette is about to be exchanged or not. The film transport mechanism of this kind is unsuitable for the so-called "fast winding", which in contemporary high efficiency cameras is normally required.
Moreover, due to the above-described complicated winding mechanism the designer of the camera employing such a known film cassette is subject to limitations in the construction of the camera especially as far as the configuration of the camera is concerned because the spacing between the two end positions of the cassette insert part, namely the starting position in union with the supply part and the detached position in the camera, has to correspond exactly to the length of a film image and is permitted only slightly to exceed this length in order to avoid unnecessary waste of the film material.
Furthermore, such a known film cassette is unsuitable for use in connection with film rolls having perforated edges such as small picture film roll having the format of 24 times 36 millimeters. For the film of such format the stroke of one film transport is preset by shifting means arranged in the camera and activated by the film transport gears. This shifting mechanism serves simultaneously for pulling a predetermined film length from the film cartridge. For construction reasons, the shifting means cannot engage the film when the above-described known film cassette is employed.